1. Technical Field
The invention relates to the determination of the sex of both human and animal subjects. More particularly, the invention relates to the instrumentation and method by which the sex and general tissue parameters of human and animal subjects can be determined noninvasively.
2. Description of the Prior Art
Near infrared (NIR) tissue spectroscopy is a promising noninvasive technology which bases measurements on the irradiation of a tissue site with NIR energy in the 700-2500 nanometer wavelength range. The energy is focused onto an area of the skin and propagates according to the scattering and absorption properties of the skin tissue. Therefore, the reflected or transmitted energy that escapes and is detected provides information about the tissue volume that is encountered.
Specifically, the attenuation of the light energy at each wavelength is a function of the structural properties and chemical composition of the tissue. Tissue layers, each containing a unique heterogeneous particulate distribution, affect light absorbance through scattering. Chemical components such as water, protein, fat, and blood analytes absorb light proportionally to their concentration through unique absorption profiles or signatures. The measurement of tissue properties, characteristics or composition is based on detecting the magnitude of light attenuation resulting from its respective scattering and/or absorption properties.
Blood Analyte Measurement
While noninvasive measurement of blood analytes, such as blood glucose concentration, has been pursued through NIR spectroscopy, the reported success and product viability has been limited by the lack of a system for compensating for structural variations between individuals that produce dramatic changes in the optical properties of the tissue sample (for example see O. Khalil, Spectroscopic and clinical aspects of non-invasive glucose measurements, Clin. Chem., vol. 45, pp. 165-77 (1999) or J. Roe, B. Smoller. Bloodless Glucose Measurements, Critical Reviews in Therapeutic Drug Carrier Systems, vol. 15, no. 3, pp. 199-241 (1998). These differences are largely anatomical and provide distinct systematic spectral absorbance features or patterns that can be related directly to specific characteristics such as dermal thickness, protein levels, and percent body fat. While the absorbance features are repeatable by subject, over a population of subjects they produce confounding nonlinear spectral variation. Therefore, differences between subjects are a significant obstacle to the noninvasive measurement of blood analytes through NIR spectral absorbance.
An apparatus and procedure for substantially reducing this problem by the classifying subjects according to major skin tissue characteristics prior to blood analyte prediction is described in S. Malin, T. Ruchti, An Intelligent System for Noninvasive Blood Analyte Prediction, U.S. patent application Ser. No. 09/359,191, filed Jul. 22, 1999. The selected characteristics are representative of the actual tissue volume irradiated and the amount of the target analyte that is sampled. By grouping individuals according to the similarity of spectral characteristics representing the tissue structure, the nonlinear variation described above is reduced and prediction of blood analytes becomes more accurate.
In human subjects, significant differences related to sex have been discovered in the skin tissue. These differences include the thickness of the dermis (see: C. Tan, B. Statham, R. Marks, P. Payne, Skin thickness measurement by pulsed ultrasound: its reproducibility, validation and variability, British Journal of Dermatology, vol. 106, pp. 657-667, (1982) and J. Bliznak, T. Staple, Roentgenographic measurement of skin thickness in normal individuals, Radiology, vol. 116, pp. 55-60 (July 1975)), the amount of fat in subcutaneous tissue (see J. Durnin, M. Rahaman, The assessment of the amount of fat in the human body from measurements of skinfold thickness, British Journal of Nutrition, vol. 21 (1967) and F. Johnston, Relationships between body composition and anthropometry, Human Biology, Vol. 54, No. 2, pp. 221-245 (May 1982)) and skin collagen and density (see S. Shuster, M. Black, E. McVitie, The influence of age and sex on skin thickness, skin collagen and density, British Journal of Dermatology, vol. 93 (1975)). The determination of subject sex therefore provides an important indication of large systematic differences in the tissue structure and composition.
Therefore, an automated method for the determination of the subject""s sex provides valuable information relevant to subject classification and determination of key tissue properties for blood analyte measurement.
Sex Determination of Animals
The determination of the sex of animal species has commercial benefit in certain industries due to the replacement of a human expert by an accurate and automated noninvasive device (see T. Miyakawa, O. Kato, Y. Koike, K. Matsunami, N. Sekiya, Fish sex discrimination equipment and method, U.S. Pat. No. 5,013,906 (May 7, 1991); K. Suzuki, Apparatus for determining the sex of a chick, U.S. Pat. No. 4,417,663 (Nov. 29, 1983); A. Frasch, R. Ugalde, Procedure for the sex determination of embryos in mammals especially applied to bovine embryos, U.S. Pat. No. 5,578,449 (Nov. 26, 1996); and W. Cheng, C. Chen, C. Hu, C. Wang, K. Choo, Process for sexing cow embryos, U.S. Pat. No. 5,876,942 (Mar. 2, 1999)). In Miyakawa et al supra. the sex of a fish is determined by examining the color of the genital gland area through visible light. In Suzuki et al supra. the sex of a chick is determined by examining the color of the anal region through the use of visible light. In Frasch et al and Cheng et al supra. methods for sexing cow embryos are detailed through a complex method of polymerase chain reactions. These methods are not extendable to human subjects or other mammals due to gross anatomical differences. Further, the methods are limited because they involve either the automated color detection of a particular often unexposed region of the animal or rely on measurements that are invasive or semi-invasive. Finally, none of the methods listed above use a near-infrared technology that penetrates the tissue to measure its internal properties. Therefore, a device for sex determination of animals needs to be developed that is accurate, noninvasive, automated, and general.
Body Composition Determination
The automated and noninvasive determination of sex provides beneficial information related to the body composition of the subject. For example, in the determination of the lean-body mass of humans, the knowledge of the subject""s sex is required prior to analysis of other anthropometric measurements (see V. Heyward, L. Stolarczyk,. Applied Body Composition Assessment, Human Kinetics, Champaign, Ill. (1996)). An automated and noninvasive device for sex determination provides a critical component for a fully automated method of body composition analysis.
It would be advantageous to provide a novel apparatus and related procedures for sex determination of human and animal subjects through NIR tissue spectroscopy that has particular benefit in several areas, including blood analyte prediction, animal sex determination, and body composition evaluation.
The invention herein provides a novel method of sex determination for animals and humans based on near-infrared measurements of the skin tissue. In addition, the invention provides fundamental information regarding gross tissue characteristics and can be used for determination of systematic and relative differences in the thickness of the dermis and the amount of subcutaneous fat at the measurement site.
The invention is a method for non-invasively determining the sex of human or animal subjects. The method uses a spectroscopic apparatus in conjunction with an optical interface to measure tissue properties and characteristics that are manifested spectrally and that vary systematically according to the subject""s sex.
The procedure for sex determination involves a calibration model that is empirically derived from a set of exemplary samples consisting of NIR tissue measurements and the actual sex of a population of subjects. The model is a set of parameters and computer generated code that is implemented to predict the subject""s sex. The prediction consists of a discrete sex determination (male or female) and one or more relative property magnitudes that reveal information regarding the tissue properties of the sampled tissue volume. These properties include but are not limited to the thickness of the dermis, the collagen content, the skin density, and the amount of subcutaneous fat at the measurement site.